error: future cannot be sent between threads safely --> $DIR/issue-71137.rs:22:14 | LL | fake_spawn(wrong_mutex()); | ^^^^^^^^^^^^^ future returned by `wrong_mutex` is not `Send` | = help: within `impl Future`, the trait `Send` is not implemented for `MutexGuard<'_, i32>` note: future is not `Send` as this value is used across an await --> $DIR/issue-71137.rs:14:26 | LL | let mut guard = m.lock().unwrap(); | --------- has type `MutexGuard<'_, i32>` which is not `Send` LL | (async { "right"; }).await; | ^^^^^ await occurs here, with `mut guard` maybe used later note: required by a bound in `fake_spawn` --> $DIR/issue-71137.rs:8:27 | LL | fn fake_spawn(f: F) { } | ^^^^ required by this bound in `fake_spawn` error: aborting due to 1 previous error